1. Field of the Disclosure
The present disclosure generally relates to a fiber reinforced composite lap joint used in assembling floor boards to produce a load carrying floor for over the road vehicular trailers and truck bodies, shipping and domestic containers, and rail wagons and flat decks. More particularly, the present disclosure includes a lap joint that is formed by the composite underlayer of at least one composite floor board being extended at one lateral edge of the board to form a flange or ledge, which is then mated with an adjacent board at a recess to form a flexible lap joint between the boards.
2. Discussion of the Background Art
Composite wood floor boards for trailer flooring are composed of a top laminated wood layer and a bottom polymer composite layer. The top layer is made of many wood strips having random lengths, which are significantly less than the length of the board. The wood strips are edge-glued to make a unitary floor board with an approximate length up to 60 feet and width of 6 to 15 inches. The ends of the wood strips are fitted with a conventional end-joint in the form of a hook, butt, finger or other mechanical or adhesive joint to make a longitudinal connection with other strips at the front ends and back ends of the wood strips. A fiber reinforced polymer composite underlayer is at least partly bonded to the bottom side of the wood layer to reinforce the laminated wood and to provide a seal for the wood and end-joints of the wood components in the boards.
A shiplap is a rectangular projecting lip running along the length at an edge of a floorboard. Typically, the lip extends along the width of a board by about ⅜ to ½ inch and has approximately half the thickness of the board. A “top shiplap” has the lip extending from the top half thickness of the board. Similarly, a “bottom shiplap” has the lip at the bottom half of the board. The crusher bead is a small semi-circular projection running along the length on each edge of a board and placed over or below a lip. When the floorboards are assembled side-by-side in a trailer such that the side edges of corresponding boards are squeezed together, the top and bottom shiplaps of adjacent boards overlap to form a seam of the shiplap joint. The shiplap joint between adjacent boards helps to transfer part of the bending and shear load applied on one board to its adjacent board. The shiplap joint also helps to prevent the entry of road debris and water or moisture into the trailer. The crusher bead provides spacing between adjacent boards to allow for lateral expansion of wood layer upon absorption of moisture by the wood. Putty is applied at the end-joints of wood strips of the boards to fill any resident gaps. In a typical vehicular trailer, container, truck body or rail wagon, henceforth generically referred to as a trailer, the floorboards are supported by thin-walled cross-members of I, C or hat sections, each having an upper flange, which span the width of the trailer and are regularly spaced along the length of the trailer. Each floor board is secured to the cross-members by screws extending through the thicknesses of the board and the upper flanges of the cross-members. The floor boards with the underlying supports and connections, together constitute the floor system. Ehrlich U.S. Pat. No. 4,703,948, is an example of prior art trailer floor assembly using shiplap joints of floor boards. The floor system of a van trailer and truck body is load rated according to Truck Trailer Manufacturers Association, Recommended Practice (TTMA RP) number 37-02, which is an industry standard in North America. In this test, a front axle loaded fork truck makes back and forth passes or load cycles on the floor in a trailer. In order to pass the test at a given load, the floor boards shall not be allowed to crack and fracture in a significant manner. In some cases, where the moisture sealing of the floor system is essential, the floor and the shiplap joints are required to maintain the initial seal after several thousand load cycles.
Even though the composite underlayer in the form of a flat sheet protects the wood and end joints at the bottom side of the wood layer, it does not protect the lateral sides of the boards in a conventional shiplap joint. Sometimes water from the roadside of the trailer can penetrate the shiplap joint either through the exposed lateral sides of end-joints in the wood layer or through any gaps between boards in the shiplap joint. Caulking or sealant is sometimes applied to the shiplap joint to form a better seal. The composite underlayer can be shaped in the form of conventional lips of the shiplap as shown in prior art U.S. Pat. No. 5,928,735. This protects the lateral wood sides of the boards, but it requires the forming of the composite shiplaps by the pultrusion process using a heated die. This process is relatively slow, costly and cumbersome to practice. In the case of a composite board with a bottom flat layer of composite, there is a need to improve the performance of the joint between adjacent boards.
A structural issue with conventional shiplaps is that the strength of the shiplap is less than the strength of the floorboard away from the shiplap. This is because the shiplap joint has two overlapping lips, namely the top and bottom lips and the top lip, which is unreinforced wood is relatively weak compared to the bottom lip with composite reinforcement. The top lip is susceptible to fatigue loads of lift truck load cycles that move cargo on the trailer floor. Further, the lips of conventional shiplaps are half the thickness of the boards and they transfer load from one lip to the other lip and thereby cause stress concentration in the inner corners of the lips. Reduction of stress concentration in the wood layer and strengthening of the joint is preferred for higher floor load rating and improved sealing at the joint.
As shown in FIGS. 1-4, conventional wood floor boards 1, 2 for over-the-road truck trailers and containers is normally manufactured with hardwoods such as ash, aspen, elm, yellow-poplar, and preferably oak, maple, birch, beech and the like, although softwoods such as Douglas fir, larch and spruce can be employed. Tropical wood species such as apitong, kapur, eucalyptus, and keruing are also used. Bamboo strips, which is typically not considered to be wood, but, which is a lignocellulosic material like wood can also be used in a generic woody floor for trailers. The generic wood floor shall be understood to be made of lignocellulosic material such as wood or bamboo. A conventional laminated wood floor board is composed of many wood strips 3, each with a length less than 10 feet. The wood strips are edge-glued to form a unitary board measuring 6 to 15 inches wide and less than 60 feet in length. The ends of the wood strips are fitted with an end-joint 4 in the form of a hook, butt, finger or other mechanical or adhesive joint to make a longitudinal connection with other strips at the front end and back end of the wood strips.
In addition, shiplap 5, 6 is typically a rectangular projecting lip running along the length at an edge of a floorboard. Typically, the lip extends along the width of a board by about ⅜ to ½ inch and has approximately half the thickness of the board. A “top shiplap” 6 has the lip extending from the top half thickness of the board. Similarly, a “bottom shiplap” 5 has the lip at the bottom half of the board. The crusher bead 7 is a small semi-circular projection running along the length on each edge of a board and placed over or below a lip. When the floorboards are assembled side-by-side in a trailer such that the side edges of corresponding boards are squeezed together, the top and bottom shiplaps of adjacent boards overlap to form a seam 8 of the shiplap joint. The shiplap joint between adjacent boards helps to transfer part of the applied load from one board to the adjacent board. The shiplap joint also helps to prevent the entry of road debris and water into the trailer, but it is not waterproof. The crusher beads provide spacing between adjacent boards for lateral expansion of wood upon the absorption of moisture. A putty is applied at the end-joints of wood strips of the boards to fill any resident gaps. All the boards are supported by thin-walled cross-members 9 of I, C or hat sections, each having an upper flange, which span the width of the trailer and are spaced apart along the length of the trailer. The ends of the cross-members are attached to the side rails 10 of the trailer. A floor seal 11 may be used between a side rail and an adjacent floor board. Each floor board is secured to the cross-members by screws 12 extending through the thicknesses of the board and the upper flanges of the cross-members.
In some closed van trailers that are more common in Europe and in some open flatbed trailers and also in open rail decks, solid wood boards 13 are used for flooring. The boards may be finger jointed 14 end-to-end to provide a long length. In some closed van trailers, a heavy duty steel or aluminum hat-channel 15, also called as omega channel, is used between boards. The channel reinforces the joint between adjacent boards, especially around a finger joint of the boards.
In a composite floor configured for a van trailer (FIG. 1), a composite underlayer 16 is bonded to the bottom side of the wood layer 17 of each board to reinforce the wood and to provide a seal for the wood and end-joints of the wood components in the laminated boards. The composite is typically a polymer composite including a polymer matrix such as epoxy, polyester, phenolic, PP or PET and includes one or more of reinforcing fibers such as glass, aramid, polyethylene, or carbon fibers. The composite layer 16 is adhesively bonded to the bottom side of the laminated wood layer 17.
A structural problem with conventional shiplaps is that the strength of the shiplap is much less than the strength of the floorboard away from the shiplap. This is because the shiplap joint has two overlapping lips 5, 6 and the top lip 6, which is unreinforced wood is relatively weak compared to the bottom lip 5 with composite reinforcement. The top lip is susceptible to the fatigue loads of lift trucks that move cargo on the trailer floor. Since the lips of shiplaps are half the thickness of the boards and they transfer load from one lip to the other lip, the load transfer causes stress concentration in the inner corners 18 of the lips upon loading of the flooring with lift trucks. The back and forth movement of the lift truck on the floor during loading and unloading of cargo can lead to cracking 19 of the top shiplap (see FIG. 5), which is not reinforced. Sometimes the bottom lip can crack at the inner corner as well. Composite floors are normally made thinner than conventional laminated wood floors for similar structural performance in a trailer, however the limitation of the thinner composite floor board is the weakness of the even more thinner shiplaps.
The present disclosure provides a composite lip at one edge of a board, which can be mated with the recess at the bottom side of an adjacent board. The composite lip is fabricated with the flat sheet composite that is also used as the underlayer of the prior art composite board. The wood layers of two adjacent boards are not lap jointed as in conventional shiplap joint. This allows for the relative deflection of one board with respect to the adjacent board without significant load transfer and improves flexibility of the joint, which in turn prevents cracking of the wood layer at the corners of the lap joint. Further, the elimination of shiplaps, allows for about 4% reduction in the wood used to make a typical 12 inch wide floor board, thus saving material and cost. The material savings is applicable to all vehicular floors, including closed van and flatbed trailers, truck bodies, containers, rail decks and wagons. By retaining the full thickness of wood at the edges of boards, the strength of the joint is superior to conventional shiplap joint. The composite lap joint provides a means to eliminate the heavy duty omega channels that are used in some floor systems. Surprisingly, the seal of the composite joint has been found to be leak free in a smoke test after conducting industry approved dynamic cyclic load test in a van trailer. That is, the use of a composite flange according to the present disclosure allows for the improved sealing of the joint and prevents water ingress into the trailer from the roadside, is stronger than a conventional shiplap joint, and saves some of the material required to make a floor board compared to conventional floor board with conventional shiplap design configuration.